Scientists have believed for years that specific genes may influence how birds migrate, and a new study of peregrine falcons offers the clearest evidence yet to support this hypothesis.

Researchers from Cardiff University in Wales and the Institute of Zoology at the Chinese Academy of Sciences in Beijing identified a gene in peregrine falcons that is usually associated with long-term memory and is more active among falcon populations with longer migration distances, leading them to believe that birds that migrate such distances require greater long-term memory capabilities.

To reach this conclusion documented Wednesday in Nature, researchers used satellite transmitters to tag 56 peregrine falcons from six locations on northern Russia’s Arctic coast and measure their migration habits for at least one entire route. To pair the route data with genetic data, the researchers also took blood samples from 35 of the falcons, with all six collection locations represented to varying degrees, and mapped the genome of each falcon.

The tracking data eventually showed that migration length varied across each group of falcons. Those that migrated from areas farther east tended to migrate much farther than those that started from farther west, closer to Europe. From about each September to October over the six years the study took place, these birds traveled anywhere between 2,000 and 11,000 kilometers to reach their destinations, at a rate of roughly 213 kilometers per day. Even after traveling such long distances, these falcons always return to within 20 kilometers of where they left. 

These differences in migration were not only apparent in the satellite data, but the genetic data as well. Each falcon’s genome contained the gene ADCY8, which is associated with long-term memory in animals and humans, but the falcons that traveled greater distances featured stronger expressions of this gene.

“What we see is an overall significant relationship between the ADCY8 variant that we found and migratory distance,” said co-author Mike Bruford, a molecular ecologist from Cardiff University’s School of Biosciences.

Scientists have long suspected that a variety of influences, or guides, set migratory birds on their arduous yearly journeys. One such guide is the earth’s magnetic fields. Bruford cautions that these other variables help birds migrate, as well, and his research simply shows that long-term memory is more significant in bird migration than was previously known. 

“Across the entire genome, when we looked at these different migratory flyways, long-distance migration was best correlated with memory as opposed to other factors,” said Bruford. “We didn’t really count on it pertaining to long-term memory, so that was a really interesting and novel insight.” 

“It’s the reason we do science,” Bruford continued, “that very occasional fleeting moment when you think, 'Oh, my god.' Just complete surprise.”

Because peregrine falcons use their long-term memory of past routes to travel the same path every year, Bruford and his team also used their migration data to estimate how climate change and habitat loss will affect falcon populations leading up to the year 2070. They found that if temperatures continue rising at their current rate, the size of each studied falcon population will likely shrink. This is especially true for those with shorter migration distances, which could stop migrating altogether, and lose most if not all of their breeding habitat.  

“We also show that the habitat is likely to change,” said Bruford. “And if they’re using memory, and if their memory also serves them, that will have disruptive consequences for their migratory behavior and pathways.” 

In future studies, Bruford and his team hope to sample genetic and tracking data from peregrine falcons from other sections of the Eurasian coast to better understand how the genetics of memory shape migratory pathways. 

The study “Climate-driven flyway changes and memory-based long-distance migration,” published March 3 in Nature, was authored by Zhongru Gu, Shengkai Pan, Zhenzhen Lin, Li Hu, Xiaoyang Dai, Jiang Chang, Yuanchao Xue, Han Su, Juan Long, Mengru Sun and Xiangjiang Zhan, Institute of Zoology at the Chinese Academy of Sciences; Sergey Ganusevich, Vasily Sokolov, Aleksandr Sokolov and Ivan Pokrovsky, Institute of Plant and Animal Ecology, Ural Division Russian Academy of Sciences; Fen Ji, State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences; and Michael W. Bruford and Andrew Dixon, Cardiff University.